1. Field of the Invention
This invention relates to a shifting arrangement for an automatic transmission of a motor vehicle, and more particularly, to an automatic transmission shifting arrangement which has a cable connecting a shift lever and a manual valve in a hydraulic control circuit to shirt the manual valve according to ranges selected by the driver through the shift lever.
2. Description of Related Art
In recent years, automatic transmissions of a motor vehicle of the type which permits a manual choice of gears in addition to automatic gear selection have been put into practical use. Such an automatic transmission automatically selects gears according to driving conditions in the automatic gear selection range and is manually shifted to intended gears selected by the driver through a shift lever. One of the automatic transmissions of this kind is known from, for example, Japanese Patent Application, laid-open to the public as Japanese Unexamined Patent Application No.7-280072. The automatic transmission described in the above mentioned publication has two shifting paths or channels for a shift lever, namely a first or range shifting channel for selecting the driving positions such as drive (D), neutral (N), reverse (R) and parking (P) positions and a second or gear shifting channel in which the shift lever can take three manual positions, namely a holding (M) position, an up-shift position and a down-shift position on opposite sides of the holding (M) position. These range and gear shifting channels extend parallel to each other in a longitudinal direction of the motor vehicle and are connected by means of a connecting channel through which the shift lever is movable between the first or range shifting channel and second or gear shifting channel.
This type of automatic transmission generally incorporates a plurality of hydraulically operated friction coupling elements such as clutches and brakes which are selectively engaged or disengaged to change a power transmission path between an engine and driving wheels and a manual valve (range shifting valve) disposed in a hydraulic control circuit operative to control supply of hydraulic pressure to and release of hydraulic pressure from the friction coupling elements so as to switch driving positions from one range to another range. The shift valve and shift lever are connected to each other by means of a shifting cable. In the range shifting channel, by way of the shifting cable, swivel movement of the shift lever is transmitted to the manual valve to shift it, thereby providing a hydraulic pressure line in the hydraulic control circuit leading to specific friction coupling elements necessary to achieve a driving position selected by the shift lever. In the case where the automatic transmission equipped with the manual gear shifting feature is provided parallel shifting channels for range and gear selection, respectively, swivel movement of the shift lever is made in the same direction in the gear shifting channel as in the range shifting channel, so that the manual valve is moved through the shifting cable even during manual gear shifting, which leads not only to heavy swivel operation of the shift lever for a manual up- or down-shift, and hence aggravation of a feeling of operation of the shift lever but to an apprehension of a deviation from a proper hydraulic pressure line for the preselected range due to movement of the manual valve. For example, in the case where the neutral (N) position is ahead of the drive (D) range selecting position in the range shifting channel and the up-shift position is ahead of the holding (M) position in the gear shifting channel, the shift lever is required to swivel in the same direction to select the neutral (N) range and to manually shift up the automatic transmission. In consequence, during manually shifting up the automatic transmission, the manual valve tends to open a hydraulic pressure line leading to a friction coupling element for achieving the neutral (N) range from a hydraulic pressure line leading to a friction coupling element for achieving the drive (D) range with an effect of causing a drop in the level of hydraulic pressure or a lack of hydraulic pressure to the latter friction coupling element.
In order to eliminate the disadvantage described above, the automatic transmission described in the above mentioned publication incorporates a mechanism for disconnecting the linkage between the shift lever and the manual valve by way of the shifting cable when the shift lever is swivelled from the range shifting channel at the drive (D) range selecting position into the gear shifting channel and reviving the linkage between the shift lever and the manual valve by way of the shifting cable when the shift lever is swivelled from the gear shifting channel at the holding (M) position into the range shifting channel.
An immanent problem in the automatic transmission described above in which connection and disconnection of transfer of movement of shift lever to the shifting cable is caused directly by movement of the shift lever between the D and M positions is that, even while the shift lever remains in the range shifting channel to select positions other than D and M positions, if the shift lever receives load in the transverse direction as strong as it is forced in the same direction, the shift lever is operationally disconnected from the shifting cable with a result of making the manual valve in the hydraulic control circuit inoperative.